Physiological Disposition and Metabolic Fate of Infused Pentoses in Man

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Abstract
Following their infusion intravenously into normal human subjects, the aldopentoses D-xylose, D-arabinose, L-arabinose, and D-lyxose disappear from blood at rates proportional to concentration. The half-times of disappearance were similar for the 4 pentoses, and averaged 71 minutes. Approximately 40% of the administered pentoses were recovered unchanged in the urine. The pentoses were distributed initially in a volume of body water somewhat larger than that of extracellular water. The rate of disappearance of xylose from blood was considerably slower than normal in two cirrhotic subjects. The infusion of each of the pentoses was accompanied by a significant drop in the serum level of inorganic phosphate, but no change in the blood levels of lactate or pyruvate were observed. Slight rises of blood glucose levels were frequently observed following infusions of D-xylose or L-arabinose. Limited studies with D-xylose-1-C14 show that this sugar is in part rapidly metabolized, giving rise to labeling of expired CO2. No significant labeling of urinary products other than of the unchanged D-xylose was detected. The metabolism of the non-excreted portions of these pentoses was discussed in terms of present concepts of carbohydrate metabolism in mammalian systems.